Well, there are even worse methods than just negative seo if you want to burn your competition out the darkest blackhat way possible.
Anyhow I wouldn't recommend you these since they are still time consuming and you wouldn't win in the longterm - and probably you would even hurt you both.

Somehow (I guess I have a pretty blackhat mindset) I still think you shouldn't harm your competitors in order to earn some money. This is just the wrong approach - learn things the right way and turn things up on your side not turnings things down on your competitors side. This little thing could literally start a cyber war in the future so better avoiding such things.